1. Field of the Invention
The present invention relates to plastic working of metals and more in particular to presses.
The press of the invention is preferably used for forging round-shaped items such as wheels, discs, flanges, tapered and spherical funnels, etc.
These types of presses are especially effective for press forming of thin-walled forgings having relatively large outer diameter to thickness ratio (with D/H being over 7).
The press of the invention is suitable for the production of forgings from ferrous and nonferrous metals by hot, semi-hot or cold die forging.
2. Description of the Prior Art
Widely known in the art are hydraulic presses in which a working tool or a die is mounted for reciprocation. In the course of operation an appreciable friction force is created at such presses between the metal being forged and the die to prevent radial flow of metal. The thinner the forging, the greater is the friction force. Thus, relatively large forces, two- to ten-fold greater than those produced during friction-free forging, are required to overcome the friction force in question. With an increase in the D/H ratio from 1 to 6, the upset force is increased approximately twice as much, and with D/H equalling 30 it increases six times. Therefore, the working of small-size forgings requires presses capable of relatively large forces and having relatively great weight and dimensions which, in turn, necessitates much floor space. In the course of forging of small-size workpieces, relatively high loads are brought about to adversely affect the wearability of dies. This in turn leads to frequent replacement of their parts with the resultant increase in the production cost of forgings and brings down the production output of the press.
Shown in FIG. 1 is a chart representing the change in the upset force at which forgings are reduced to relatively small sizes depending on the movement of the die. Plotted along the x-axis is the die movement .DELTA.H from the moment of initial upsetting of the forging, and plotted along the y-axis is the upset force P. Curve 1 at this chart is given to show the change in the upset force during translatory motion of the working tool. As is seen from the chart, the upset force sharply increases with the decrease in the height of a forging.
There is known a hydraulic press which comprises a frame made up of two crossheads rigidly interconnected by means of uprights. Mounted in guides one above the other between the uprights are two rams. One of the rams has a built-in nut with a non-self-stopping thread for forced engagement with a screw carrying a die holder. The die holder is mounted for rotaion in the other ram. Translatory motion of the screw is enabled by connecting the latter to the movable link of a hydraulic cylinder brought in communication with a fluid source and positioned on one of the crossheads.
The ram with the built-in nut has projections formed over its periphery. Fixed on the frame within a certain distance from the projections (when in initial position) are stops against which the ram with the nut is thrust up with its projections to permit forced engagement of the nut with the screw (cf. USSR Inventor's Certificate No. 706,173).
In the above-described press, the die holder with the die is capable of performing in the process of forging not only translatory motion, but rotary motion as well. The press of this type is intended for combined forging and twisting operations, during which the conditions of the contact friction between the workpiece and the die are due to change, with tangentially acting shear strain taking place in the metal under deformation. Such deformation of metal may lead to a multiple decrease in the working force and loads acting on the die, and to more uniform filling of the die impression with metal.
When external loads are applied to the workpiece under deformation normally or tangentially thereto, the process of deformation is sharply intensified. This, in all likelihood, is associated with the rotation of the friction vector and with the resultant decrease in the radial component thereof. In addition, a shear strain is produced under the action of tangential component of the friction vector. As a result, a required deforming force is reduced 2 to 10 times depending on the size ratio (or diameter to thickness ratio, indicated as D/H) in the workpieces, whereby a possibility is offered to produce round-shaped forgings with thin walls and bottom. Rotation of the working tool permits uniform filling of the die impression with metal and facilitates its operation during final forging. By reducing the influence of the contact forces of friction it becomes feasible to minimize the adverse effect of the eccentricity in the positioning of the workpiece relative to the die axis, resultant from the nonuniform filling of the die cavity with metal. This can be seen from the height of the flash formed at the butt end of the workpiece, as well as from the width of the flash formed over the entire perimeter of the forging. A decrease in the size of flash, as well as in the thickness of sections for broaching, makes it possible to enhance the metal utilization factor.
A decline in the intensity of the action force, as well as in other effects involved in the die forging and twisting, is direclty associated with the diameter to thickness ratio of each forging. FIG. 1 shows curves representing the change in the upset force under the action of a rotating tool (Curves 2, 3 and 4) at different working tool angular to translatory velocity ratio, with curve 4 being obtained at a higher ratio than for curve 2.
The prior-art press permits the die forging to be combined with twisting in the event when the ram with the built-in nut is brought to a stop. This is made possible when the projections of the ram with a built-in nut reach the stops on the frame. The angle of rotation of the die holder is determined from the following formula ##EQU1## where .DELTA.H is the value indicating translatory motion of the die holder when the ram with a built-in nut is brought to a stop;
S is the feed of the screw.
In the known hydraulic press the angle .phi. of rotation of the die holder during its translatory motion .DELTA.H is relatively small. This can be explained by the fact that in the given press construction use is made of a non-self-stopping thread with an appreciable lead. Since small torsion angles make it impossible to substantially reduce the force of forging, the production range of the press is confined along with the type and size of forgings being produced.
In the known hydraulic press a relatively great force P.sub.1, brought about by the pressure of the working fluid, acts on the movable link or plunger of a hydraulic cylinder, and on the frame. The force P.sub.1 is to overcome resistance P.sub.2 of the metal being deformed to the translatory motion of the die holder, as well as a force P.sub.3 of the axial movement of the screw relative to the nut, which is brought about by the retarding action of torque M, hence: EQU P.sub.1 =P.sub.2 +P.sub.3
From the above it follows that the rated force P.sub.1 of the press is greater than the force P.sub.2 of the axial motion of the die holder by a value of the force P.sub.3 equal to: P.sub.3 =2.pi.M/S. At relatively great torque M, the value of P.sub.3 will be relatively high to result in the increase of the rated force of the press and in a greater amount of metal required for its manufacture.
It is therefore an object of the present invention to expand the production range of the press or, in other words, to produce forgings with a diameter to thickness ratio substantially greater than that in the known press of the same rated force.
Another object of the invention is to reduce the amount of metal normally required for the manufacture of the prior-art press used for producing forgings of similar type and size.
Still another object of the invention is to reduce the floor space required for the press.
These and other objects of the present invention are accomplished by the provision of a press comprising a frame made up of two cross heads rigidly interconnected by means of uprights with two rams mounted therebetween one above the other and of which one is fitted with a nut having a non-self-stopping thread forcibly engaged with a screw rigidly connected with a die holder mounted for rotation in the outer ram and geared to a drive for its translatory motion, wherein, forced engagement of the nut with the screw is effected through the agency of a drive provided to actuate the ram with the built-in nut and controlled from the drive of the die holder, with a clearance of sufficient size being provided between the rams to permit a specified angle of rotation of the die holder.
If a hydraulic cylinder communicating through a pressure line with a fluid source is used as the drive for the translatory motion of the other ram, the ram with a built-in nut is preferably actuated by means of at least one auxiliary hydraulic cylinder brought in communication with a fluid source through a pressure line and connected by its movable link to this ram.
This permits a hydraulically operated press to be used for die forging of workpieces by a rotating tool, while the hydraulic press in communication with a fluid source ensures the required translatory motion of the nut relative to the screw and, consequently, a specified angle of rotation of the die holder. In this way it becomes possible to achieve optimal parameters of forging or, in other words, to bring down the axial force of forging to a specified level.
In addition, it becomes possible to prevent rotation of the movable links or rods of hydraulic cylinders, and thereby to increase service life of their sealings.
Two auxiliary hydraulic cylinders are preferably provided to actuate the ram with the built-in nut, which cylinders are arranged in symmetry with the hydraulic cylinder for translatory motion of the die holder on one and the same crosshead.
Such structural arrangement permits all hydraulic cylinders to be arranged on one crosshead and facilitates assembly and servicing of the press.
It is preferred to have a fluid pressure gauge set in the pressure line communicating the hydraulic cylinder for actuating the die holder with a fluid source while a pressure line communicating at least one auxiliary hydraulic cylinder with a fluid source is preferably furnished with a variable orifice and a pressure valve responsive to a signal from the pressure gauge.
Providing the pressure gauge for controlling the operation of the auxiliary hydraulic actuators would enable rotation of the die holder at a given force to forge, when it is essential to set in rotation the working tool. It has been found from an analysis of the curve 1 shown in FIG. 1 that the greatest force to forge is produced at the end of forging. Hence, the die forging and twisting could be recommended for use precisely at this moment of deformation. Such mode of die forging permits the working stroke of the ram with the built-in nut to be utilized most efficiently and power losses due to twisting to be reduced. The provision of a variable orifice makes it possible to control the speed of rotation of the die holder, which further enhances efficiency of the working stroke of the ram with the built-in nut.
Advantageously, the pressure line communicating the hydraulic cylinder for translatory motion of the die holder is made to pass through at least one auxiliary hydraulic cylinder wherefor the rod end of the latter is brought in communication with the head end of the hydraulic cylinder, with the ratio of the cross-sectional area of the head end of the hydraulic cylinder to the cross-sectional area of the rod end of at least one auxiliary hydraulic cylinder being equal the ram with a built-in nut to die holder speed ratio.
This press construction allows for such mode of forging that would permit the die holder angular to translatory speed ratio to be maintained constant over the entire period of forging. In addition, owing to the boosting effect it is possible to create a higher pressure in the head end of the hydraulic cylinder for translatory motion of the die holder than in the fluid source, whereby it becomes feasible to reduce dimensions of both the hydraulic cylinder and press as a whole.
The press is preferably provided with one auxiliary hydraulic cylinder adapted to actuate the ram with a built-in nut and mounted on a common crosshead coaxially with the hydraulic cylinder provided to enable translatory motion of the die holder and positioned on the crosshead, with a supporting bearing being set between the ram and the die holder.
Such structural arrangement makes it possible to reduce the frame in height and width, to unload the frame, and thus to bring down the amount of metal required for its manufacture.
Both rams are preferably interconnected and a clearance of sufficient size permitting a specified angle of rotation of the die holder is formed between the opposite ends of the nut and the die holder.
Such a structural arrangement is effective where it is necessary to obtain relatively small torsion angles and, consequently, to move the ram with a built-in nut relative to the die holder. As a result it becomes feasible to reduce dimensions of the press and simplify its construction. Such press construction is advantageously used for die forging of workpieces in three stages, namely: upsetting of the workpiece, its die forging and cutting off flash or fins. The forging operation is preferably combined with twisting, while two other operations are carried out with the aid of an advancing tool fixed by auxiliary die holders on the ram in symmetry with the rotating die holder.
With the rams made into a single unit, the press construction is rendered space-saving and permits the die holders for auxiliary dies to be mounted on the ram.
Where the drive provided to enable translatory motion of the die holder comprises, arranged on one of the crossheads and connected to an electric motor, a shaft with an eccentric coupled through a connecting rod to a screw carrying a die holder, the drive of the ram with a built-in nut is preferably provided with two connecting rods arranged in symmetry with the connecting rod coupled to the nut, and connected with the ram and geared to the shaft.
Thus a crank press may be suitably used for die forging by means of a rotating tool and the drive of the ram with a built-in nut permits a required translatory motion of the nut relative to the screw, whereby a specified angle of rotation of the die holder is obtained to produce a forging of a preset size. In this way it becomes possible to secure optimal parameters of forging by reducing its axial force P.sub.2.
The gearing of the shaft with the connecting rods, coupled to the ram with a built-in nut, is preferably effected through the agency of two eccentrics positioned on the shaft in symmetry with the eccentric and turned relative thereto in the direction opposite to the direction of rotation of the shaft through an angle sufficient to permit a specified angle of rotation of the die holder.
Such structural arrangement permits the simplest type of gearing of the shaft with the connecting rods coupled to the ram. With two eccentrics being turned relative to the central shaft in the direction opposite to the direction of its rotation, the gearing of the press is such that permits the die holder angular to translatory speed ratio to be sharply increased toward the end of forging with the resultant decrease in the force to forge and more uniform filling of the die impression with metal.
The gearing of the shaft to the connecting rods, coupled to the ram with a built-in nut is preferably effected through an auxiliary shaft mounted on the other crosshead of the frame and provided with two eccentrics connected with the ram coupled to an auxiliary electric motor and through a train of gears with a shaft, with the angle in the direction of rotation of the shaft between the axes of the press and the eccentric of the shaft being greater than the angle between the axes of the press and the eccentrics of the auxiliary shaft by a value sufficient to permit a specified angle of rotation of the die holder.
Such a structural arrangement makes it possible to reduce the press in width by reducing the length of the press. At the same time, rigidity of the press may be increased and the load acting thereon decreased by reason of the fact that the effort required to rotate the die holder is transmitted through an auxiliary shaft. This also reduces the torque transmitted from the drive to the shaft, which facilitates its operation.
The gearing of the shaft to the connecting rods, coupled to the ram with a built-in nut, is preferably effected through the agency of the connecting rod linked with a screw wherefor a pin is mounted therein away from the longitudinal axis of the connecting rod at a distance sufficient to permit a specified angle of rotation of the die holder, which pin is coupled to the connecting rods linked with the ram.
Such a structural arrangement makes it possible to use the shaft with a single eccentric, which simplifies construction of the press and contributes to its high rigidity.
The gearing of the shaft to the connecting rods coupled to the ram with a built-in nut, is preferably effected by means of two rockers arranged in symmetry with the eccentric cooperating with the connecting rod coupled to the screw to enable its translatory motion, each of the rockers having one of its arms coupled to the connecting rods and the other arm through at least one intermediate link to the connecting rod joined with the screw away from the axis of the eccentric at a distance sufficient to permit a specified angle of rotation of the die holder.
Such a structural arrangement substantially improves the gearing of the press and thus provides for the most effective movement of the ram with a built-in nut as well as rotation of the die holder to enable optimal process parameters.